This invention relates to dispensers and, more particularly, to a hand-held dispensing device which can repeatably deliver a precise quantity of liquid.
There have been previously devised various types of apparatus for repeatably delivering a precise amount of liquid. Many types of hand-held syringes are capable of this task. However, in most cases it is necessary to refill the syringe after each use or to provide a number of different "stop" positions for the syringe plunger. This latter technique requires special operator control and generally yields only a very limited number of samples for each full stroke of the plunger.
Responsive to the need for a repeatable liquid delivery system having the capacity for delivering large numbers of samples without refilling, there have been devices various types of plunger bottle dispensers, examples being disclosed in U.S. Pat. Nos. 3,191,807; 3,430,813; 3,730,398; and 3,741,444. Typically, these units comprise a plunger and a first check valve which allows liquid to pass into a chamber when the plunger is released (i.e., drawn back by action of a biasing sprrng). A second check valve al ows the liquid to be delivered when the plunger is depressed, and a relatively large capacity bottle serves as the source from which liquid is drawn in through the first check valve. This type of bottle dispenser system is found to operate satisfactorily in some applications, but there is a degree of inconvenience associated with the size and bulk of the bottle and the frequent necessity of bringing test tubes or vessels to the vicinity where the bottle is located.
In my U.S Pat. No, 4,046,291, there is disclosed a device for pipetting and/or diluting wherein the supply of liquid reagent is integral with the device itself; i.e., the supply of reagent is contained within an enclosure defining a back chamber of the device which surrounds the plunger. The plunger has a communicating passage between the back chamber and a front chamber that is in front of the plunger. A one-way valve restricts flow in the communicating passage to occur only from the back chamber toward the front chamber. When the plunger is released, the liquid reagent is drawn into the front chamber, and thereafter it is dispensed when the plunger is depressed. Each time the plunger is released, an aliquot of reagent is drawn into the front chamber for subsequent dispensing.
It is an object of the present invention to provide a dispensing device of the type disclosed in my above-referenced U.S. Pat. No, 4,046,291, but which is an improvement thereon. In particular, it is an object of the invention to provide a hand-held dispenser which can repeatably deliver a precise quantity of liquid reagent and has an improved valve system, which is easy to load with a bulk supply of such reagent, which has improved venting of the reagent supply, and which is easy to handle and use, with little manual dexterity being required.